Telephone trunk circuit



March 18, 1930.

H. B. JOHNSON 1,751,207

TELEPHONE TRUNK CIRCUIT v Filed April 26, 1928 2 Sheets-Sheet l Lu. //VVENTOH f/msmr 15. Jam 50m I B Arm/WE) March 18, 1930. H. B. JOHNSON- 1,751,207

TELEPHONE TRUNK CIRCUIT Filed April 26, 1928 2 Sheets-Sheet 2 wvf/vrafis HERBERT 5f Jam/.9041

ATTORNEY Patented Mar. 18, 1930 V UNITED STATES HERBERT B. JOHNSON, on FLUSI-IING, NEW voRK, ASSIGNOR To ELL TELEPHONE PATENT oFFIcs LABORATORIES, INCORPORATED, OF NEW YORK, N. '17., A CORPORATION'OF YORK Application: filed Apri1'26,

Thisinvention relates to telephone trunking systems whereby connections are established between a calling and ,a called line through two trunk-lines in tandem and more particularly to atandem trunk circuit for establishing connections between a toll operators cord circuit and the outgoing end of a 'toll switching trunk at a tandem operators position. v 1O It has been the practice for a number of.

- years to complete toll connectionsto called subscribers lines terminating at B or toll switching positions over what are known as tollswitching trunks a k The method of operation of suchya system, arranged to work on what is known as a; straightforward basis, is for the toll-operator. to plug her cord circuit into a switching trunk to the desired exchange and, when the B or toll switching operator is connected-to the trunk, request that the incoming end. of the trunk be connected with the called subscribers line. TheB operator performs this function but does not ring the subscriben this operation being left under control .of the toll operator. i p This method of operationrequires that the toll operator have complete supervision .of the connection. That is, the called supervisory lamp of the toll cord must light when the B operator connects the trunk to the sub scribers line, remain lighted until the subf scriber answers at which time it will be, ex-

tinguishedand must again, light when the called subscriber hangs up. Such a system of supervision between a B and a toll position is disclosed in U. s Patent 1,812,? 73" to R. S. Wilbur. I a

In the present system, arranged to work on a straightforward basis, a single toll office serves a plurality of local exchanges over a single group of toll trunk. lines extending from thetoll'office to a concentrating posi-. tion, called a tandem position, from which point groups of toll switching trunks extend to the various local ofl'ices.

In its broadest aspect, the object 'of the invention is to efiect economies intrunk facilities and in its attainmenta specific object of the invention is to enable supervisory signals now described is shown gust 12,191a.

TELEPHONE TRUNK CIRCUIT 1928. Serial No. 272,898.

to be transmitted from the toll switching trunk, through the tandem position and over the tandem trunk, to the toll operatons cord an arrangementnfor tandem toll trunks such that supervisory signals, transmitted back over the toll switching trunk fromithe local exchange to the tandem ofiice, are automati cally repeated and retransmitted over the tandemtrunk to controlisupervisory ap paratusat the toll office.

o Other features of the invention will appear from. the following description. 1

The embodiment ofthe invention} to be by the accompanying drawing of which: i 1

Fig. 1 represents a straightforward tandem trunk circuit extending from atoll operatorsposition to a tandem operators p-osition and Fig. 2 represents a standard tollswitching Fig. 1 to a B or toll switching operators po- 2 is similarito the trunk circuit D disclosed in the patent to Nilbur 1,312,773,dated Au- In systems of the character described, the

toll operator, whose cord circuit C is shown at the left ofFig. 1, receives from a recording operator, or otherwise, a ticket giving the information as to the calling subscriber and the called subscribersnumber or name or both. The tolloperator then inserts the plug 1 of her cord circuit in the jack 2 ofthe tandem trunk circuit T extending from the toll office to a tandemioffice represented by the trunk extending from the tandem position of trunk equipment-at the right of the vertical broken line a-a, whereupon relay 3 operates in a circuit which may be traced from.

batteryyleft hand winding of relay 3, contacts 4 of relay. 5, lower winding of retard coil 6, ring conductors of trunk T, ring spring and contact of jack 2 and plug 1, respectively, ring conductor of the cord circuit C, lower winding of retard coil 7, winding of relay 8, upper Winding of retard coi17,tip conductor of cord C and trunk T, upper winding of'retard coil 6, contacts 9 of relay and right hand winding of relay 3 to ground.

- 'Relay 3 thereupon operates and completes energizing circuits for relays 5 and 11 and closes a circuit fors'teadily lightingv guard and disconnect lamp 12- Although relay 8 maybe immediately Operated, thereby clos- "ing the circuit of the toll cord supervisory *lampjl0,yet the immediateoperation of relay 5 disconnects battery and ground from the trunk and causes therelay 8 torelease at once, thereby opening the lamp circuit and preventing this lamp from being lighted at this time as a signal to the toll operator to start ringing. Relay 5 in operating, however,

closes its contacts '13, thereby completing a' holding circuit for relay 3,which relay therefore is not released at this time.

' Relay 11, in operating, closes its contacts 14 thereby operating relay 15. Relay 15 operates and closesan obvious circuit for relay 17,

which relay closes at its left hand contacts a connection fromthe trunk to thecontrol circuit, not shown, and connects battery, supplied over contacts 16 of relay 11, through the left hand winding and contacts of relay 18 and contacts 19 of relay 17, to the control circuit-which thereupon functions and causes three short impulses of tonecurrent, commonly referred to as Zips, to the trunk which are heard by the toll operator and understood by her as a signal to pass the exchange designation and numberof. the called line.

Relay'18, however, does'not operate at this-time due to a high resistance in the control circuit. I V V After the order tone or zips have been transmitted relays in the'control circuit function to connect the operators telephone set,

not shown, tothetrunkoverthe left hand contacts of relay 17. Further," relay 17 in operating closes its outer right contacts and completes a circuit forfiashing the guard and disconnect lamp 12which, up to this 'time, has been burning steadily. This is ac-" complished by periodically shunting the lamp with the winding of the slow releasing relay '20 under control of a constantly operating circuit closing'device 21. The'flashing of lamp 12 indicates to the tandem operator that she is connected to trunk T. I

4 Relay 20 operates following the first flash of lamp 12-and, being slow to release, holds up oversubsequent flashing, thereby causing pilot lamp 22 to burn steadily; As soon as the tandem operator ascertains the oflice designation and number of the called subscribers line, she selects a toll switching trunk extending to the. desired oflice, which we will assume is the trunk S shown in Fig. 2' and j then passes the information received from the tolloperator toothe B or switching operatorin any desired manner which, as it forms no part of the present invention, Will not be further discussed.

.When the tandem operator inserts the plug 23 in jack 24 of the switching trunk the sleeve relay 25 of the tandem trunk operates in "an I obvious circuit and transfers the tip of the plug 23 from the busy test lead 26 to the tlp conductor of the trunk, opens the circuit of the lamp 12 thereby extinguishing it, operates relay 18 by closingwcontacts 27 and 28 and also completes, at its contacts- 28, atoming circuit for relay 5, which can be traced from ground, left hand contacts of relay 3,

right hand winding of relay 5 and contacts 28 of. relay 25 to battery. The reason for "holdingrelay 5'0perated at; this time is to prevent battery and ground, standing on the outer contacts of relay 5, from being con nectedvto the trunk which would lightlamp circuit from lamp 12, which'the'reupon lights steadily again. 4 7

With plug 23 in jack 24, battery and ground is supplied over the switching trunk S to option. This circuit can'be traced from battery, right hand winding of relay 30, contacts 31,.

relay 32, upper left winding of repeating coil 33, tip conductor of trunk S and tip spring ofjack '24, tip contact ofplug .23, contacts 41 0f relay 25, contacts 34 of relay 35,-'contacts 36 of relay 37 upper winding ofretard coil 38, winding ofrelay29, lower winding ofret ard coil 38, contacts 39 of relay 37, lower normal contacts of relay 35,ring;- contact of plug 23, ring spring of'jack 24, ring conductor of trunk S," lower left hand winding of repeating coil 33, contacts 40 of relay 32and left hand winding'f of relay 30 to ground crate the line relay 30' at the switching posi- Relay 30'operates and closes' its contacts 42,

thereby operating relay 32 -'and lighting the guard and disconnect lamp 43; The opera tionof relay 32 immediatelydisconnects battery and ground from the trunk S in order not to operate relay 29 at the tandem 'oflice at this time, which, as before explained, would cause a ringing signal to be transmitted Ito the toll operatorY 'Relay 32-in ope'rating also closes its'contacts 44, thereby'completing an obvious holding circuit-for relay 30, which must not release at this timeJi When the switching operator completes the call to the'desir'ed subscribers line L by inserting the plug 45 into the jack 46, sleeve relay 47 operates in an'obvious circuit and connects the ring of thetrunk through to the" repeating coil 33. The lower armature of relay 47, which is attracted when the winding of this relay is energized, opens the circuit through the right hand winding of relay 32 and lamp 43, thereby causing relay 32 to be.

otlice, as previously described and energizes relay 29. Relay 29 in operating short-circuits the right hand winding of relay 5 and causes this relay to release, which in turn reconnects battery and ground to the trunk T, which causes relay 8 in the toll cord circuit to attract its armature and light lamp 10. The toll operator recognizes this as a signal that the distant end of the switching trunk, to which the tandem trunk is connected, has been plugged into the called line and that she may now ring the subscriber by operating the ringing key K associated with the cord circuit in use.

Ringing current applied to the trunk T by the lrey K causes actuation of the relay 48 at the tandem end of the trunk, which in turn operates relay 37. Relay37 splits the trunk by opening contacts 36 and49 and connects locally supplied ringing current over its alternate contacts to the switching trunk S. When the trunk was split by the operation of relay 37 relay 29 released, thereby removing the short-circuit from relay 5, which relay thereupon reoperates.

Ringing current applied to the switching trunk at the tandem position causes relay 50 at the distant end of the switching trunk to operate, which closes a circuit from ground through the winding of relay 51 and the left hand winding of relay 52 to battery. Relay 51 operates and relays ringing current to the called line L to operate the called subscribers bell. Relay 32 also reoperates which removes battery and ground from the switching trunk during the ringing interval and closes the holding circuit for relay 30. When the ringing key K is released, relays 48 and 37 release. Relay 37 in releasing disconnects ringing current from the switching trunk which permits relay 50to release. This relay releases relay 51, which disconnects ringing current from the called line. Relay 50 also releases relay 32, which reconnects battery and ground to the trunk, which causes relay 29 to again operate, which once more shortcircuits relay 5 and causes it to again release.

When the called subscriber answers relay 52 operates, which completes an energizing circuit for relay 32, which can be traced from battery through the left hand winding of relay 32, contacts of relay 52, right hand winding of relay 52 and contacts 42 of relay 30 to ground. Relay 32 operates and again disconnects battery and ground from the trunk S, which releases relay 29, thereby operating relay 5 to disconnect battery'and ground from the trunk, which .causes the cord supervisorylamp 10 to be extinguished as a signal that the calledxsubscriber has answered. g

In case the outgoing switching trunks of any particular group at thetandemposition are busy the tandem operator inserts plug 23 into the busy-jack'53, whereuponintermittent battery and ground is appliedsto the trunk and causes relay 29 toalternatelyoperate and release, thereby intermittently .re-

leasing relay 5, which alternately connects and disconnects battery and groundi-ito the trunk-to flash lamp 10in the toll cord circuit.

In case the subscribers line is *busy the switching operator-will insert plug 45 into busy-jack 54, which alternately operates relay 52, which in turn causes relay 32 to intermittently apply battery and ground-to the trunk S, leading back to the tandem position,

where it causes relay 29 to flash the toll cord supervisory lamp 10 in the manner just described. V

When the called subscriber hangs up, relay 52 releases, which in turn releases relay 32'and causes the lamp 10 in the toll cord to light as a disconnect signal. When the toll operator disconnects relay 3 is released, which in turn releases relay 11. Relay 11 released causes relay 35 to operate, which lights the guard and disconnect lamp 12 in an obvious circuit.

thereby opening the circuit of relay 30, which 7 The tandem operator noting this s1gnal dlsconnects from the switching trunk;

releases and closes its contacts 55, which 7 thereupon causes lamp 4:3 to light as a disconnectsignal to the switching operator.

When the tandem operator disconnects by removing plug 23 from ack 24, relay 251releases, which releases'relay 35 and extin guishes lamp 12, whereupon the circuit restores to normal. i 1

What is claimed is:

1. Ina telephone system, a toll-operators position, a cord circuit thereat, a tandem position, a tandem trunk line interconnecting said toll and tandem positions, a switching position, a switching trunk interconnecting said tandem and switching positions, means for interconnecting said trunks at saidtandem position, called lines outgoing from said switching position, means for connecting said switching trunk with one of said called lines, a supervisory relay associated with saidv cord circuit, a first relay associated with said tandem trunk at the tandem position end thereof, a circuit including a source of current, a winding of said supervisory relay and contacts of said first trunk relay, a second relay associated with said tandem trunk adapted to disable said first relay, and a third relay associated with said switching trunk and controlled by said'called line for V controlling said second relay.

' 2. In a telephone system, a cord circuit, a called line, a tandem trunk and a toll switching trunk for interconnecting said cord circuit and said called line, a supervisory relay associated with said cord circuit, a first relay associated With the incoming end only 7 of said tandem trunk, an energizing circuit for said supervisory relay including contacts of said first relay, means at the incoming end of said tandem trunk for controlling said I first relay, and means associated With said.-

switching' trunk, controlled by said called line, forv controlling said first means.

In Witness whereof, I hereunto subscribe .my name this 23rd day of April, 1928.

HERBERT B. JOHNSON. 

